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/*

  Stockfish, a UCI chess playing engine derived from Glaurung 2.1

  Copyright (C) 2004-2008 Tord Romstad (Glaurung author)

  Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad

  Copyright (C) 2015-2018 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad

  Stockfish is free software: you can redistribute it and/or modify

  it under the terms of the GNU General Public License as published by

  the Free Software Foundation, either version 3 of the License, or

  (at your option) any later version.

  Stockfish is distributed in the hope that it will be useful,

  but WITHOUT ANY WARRANTY; without even the implied warranty of

  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License

  along with this program.  If not, see <http://www.gnu.org/licenses/>.

*/

#include <algorithm>

#include <cassert>

#include <cstring>   // For std::memset

#include <iomanip>

#include <sstream>

#include "bitboard.h"

#include "evaluate.h"

#include "material.h"

#include "pawns.h"

namespace {

  const Bitboard Center      = (FileDBB | FileEBB) & (Rank4BB | Rank5BB);

  const Bitboard QueenSide   = FileABB | FileBBB | FileCBB | FileDBB;

  const Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;

  const Bitboard KingSide    = FileEBB | FileFBB | FileGBB | FileHBB;

  const Bitboard KingFlank[FILE_NB] = {

    QueenSide, QueenSide, QueenSide, CenterFiles, CenterFiles, KingSide, KingSide, KingSide

  };

  namespace Trace {

    enum Tracing {NO_TRACE, TRACE};

    enum Term { // The first 8 entries are for PieceType

      MATERIAL = 8, IMBALANCE, MOBILITY, THREAT, PASSED, SPACE, INITIATIVE, TOTAL, TERM_NB

    };

    double scores[TERM_NB][COLOR_NB][PHASE_NB];

    double to_cp(Value v) { return double(v) / PawnValueEg; }

    void add(int idx, Color c, Score s) {

      scores[idx][c][MG] = to_cp(mg_value(s));

      scores[idx][c][EG] = to_cp(eg_value(s));

    }

    void add(int idx, Score w, Score b = SCORE_ZERO) {

      add(idx, WHITE, w); add(idx, BLACK, b);

    }

    std::ostream& operator<<(std::ostream& os, Term t) {

      if (t == MATERIAL || t == IMBALANCE || t == Term(PAWN) || t == INITIATIVE || t == TOTAL)

          os << "  ---   --- |   ---   --- | ";

      else

          os << std::setw(5) << scores[t][WHITE][MG] << " "

             << std::setw(5) << scores[t][WHITE][EG] << " | "

             << std::setw(5) << scores[t][BLACK][MG] << " "

             << std::setw(5) << scores[t][BLACK][EG] << " | ";

      os << std::setw(5) << scores[t][WHITE][MG] - scores[t][BLACK][MG] << " "

         << std::setw(5) << scores[t][WHITE][EG] - scores[t][BLACK][EG] << " \n";

      return os;

    }

  }

  using namespace Trace;

  // Evaluation class contains various information computed and collected

  // by the evaluation functions.

  template<Tracing T = NO_TRACE>

  class Evaluation {

  public:

    Evaluation() = delete;

    Evaluation(const Position& p) : pos(p) {}

    Evaluation& operator=(const Evaluation&) = delete;

    Value value();

  private:

    // Evaluation helpers (used when calling value())

    template<Color Us> void initialize();

    template<Color Us> Score evaluate_king();

    template<Color Us> Score evaluate_threats();

    int king_distance(Color c, Square s);

    template<Color Us> Score evaluate_passed_pawns();

    template<Color Us> Score evaluate_space();

    template<Color Us, PieceType Pt> Score evaluate_pieces();

    ScaleFactor evaluate_scale_factor(Value eg);

    Score evaluate_initiative(Value eg);

    // Data members

    const Position& pos;

    Material::Entry* me;

    Pawns::Entry* pe;

    Bitboard mobilityArea[COLOR_NB];

    Score mobility[COLOR_NB] = { SCORE_ZERO, SCORE_ZERO };

    // attackedBy[color][piece type] is a bitboard representing all squares

    // attacked by a given color and piece type. Special "piece types" which are

    // also calculated are QUEEN_DIAGONAL and ALL_PIECES.

    Bitboard attackedBy[COLOR_NB][PIECE_TYPE_NB];

    // attackedBy2[color] are the squares attacked by 2 pieces of a given color,

    // possibly via x-ray or by one pawn and one piece. Diagonal x-ray through

    // pawn or squares attacked by 2 pawns are not explicitly added.

    Bitboard attackedBy2[COLOR_NB];

    // kingRing[color] is the zone around the king which is considered

    // by the king safety evaluation. This consists of the squares directly

    // adjacent to the king, and (only for a king on its first rank) the

    // squares two ranks in front of the king. For instance, if black's king

    // is on g8, kingRing[BLACK] is a bitboard containing the squares f8, h8,

    // f7, g7, h7, f6, g6 and h6.

    Bitboard kingRing[COLOR_NB];

    // kingAttackersCount[color] is the number of pieces of the given color

    // which attack a square in the kingRing of the enemy king.

    int kingAttackersCount[COLOR_NB];

    // kingAttackersWeight[color] is the sum of the "weights" of the pieces of the

    // given color which attack a square in the kingRing of the enemy king. The

    // weights of the individual piece types are given by the elements in the

    // KingAttackWeights array.

    int kingAttackersWeight[COLOR_NB];

    // kingAdjacentZoneAttacksCount[color] is the number of attacks by the given

    // color to squares directly adjacent to the enemy king. Pieces which attack

    // more than one square are counted multiple times. For instance, if there is

    // a white knight on g5 and black's king is on g8, this white knight adds 2

    // to kingAdjacentZoneAttacksCount[WHITE].

    int kingAdjacentZoneAttacksCount[COLOR_NB];

  };

  #define V(v) Value(v)

  #define S(mg, eg) make_score(mg, eg)

  // MobilityBonus[PieceType-2][attacked] contains bonuses for middle and end game,

  // indexed by piece type and number of attacked squares in the mobility area.

  const Score MobilityBonus[][32] = {

    { S(-75,-76), S(-57,-54), S( -9,-28), S( -2,-10), S(  6,  5), S( 14, 12), // Knights

      S( 22, 26), S( 29, 29), S( 36, 29) },

    { S(-48,-59), S(-20,-23), S( 16, -3), S( 26, 13), S( 38, 24), S( 51, 42), // Bishops

      S( 55, 54), S( 63, 57), S( 63, 65), S( 68, 73), S( 81, 78), S( 81, 86),

      S( 91, 88), S( 98, 97) },

    { S(-58,-76), S(-27,-18), S(-15, 28), S(-10, 55), S( -5, 69), S( -2, 82), // Rooks

      S(  9,112), S( 16,118), S( 30,132), S( 29,142), S( 32,155), S( 38,165),

      S( 46,166), S( 48,169), S( 58,171) },

    { S(-39,-36), S(-21,-15), S(  3,  8), S(  3, 18), S( 14, 34), S( 22, 54), // Queens

      S( 28, 61), S( 41, 73), S( 43, 79), S( 48, 92), S( 56, 94), S( 60,104),

      S( 60,113), S( 66,120), S( 67,123), S( 70,126), S( 71,133), S( 73,136),

      S( 79,140), S( 88,143), S( 88,148), S( 99,166), S(102,170), S(102,175),

      S(106,184), S(109,191), S(113,206), S(116,212) }

  };

  // Outpost[knight/bishop][supported by pawn] contains bonuses for minor

  // pieces if they can reach an outpost square, bigger if that square is

  // supported by a pawn. If the minor piece occupies an outpost square

  // then score is doubled.

  const Score Outpost[][2] = {

    { S(22, 6), S(36,12) }, // Knight

    { S( 9, 2), S(15, 5) }  // Bishop

  };

  // RookOnFile[semiopen/open] contains bonuses for each rook when there is no

  // friendly pawn on the rook file.

  const Score RookOnFile[] = { S(20, 7), S(45, 20) };

  // ThreatByMinor/ByRook[attacked PieceType] contains bonuses according to

  // which piece type attacks which one. Attacks on lesser pieces which are

  // pawn-defended are not considered.

  const Score ThreatByMinor[PIECE_TYPE_NB] = {

    S(0, 0), S(0, 33), S(45, 43), S(46, 47), S(72, 107), S(48, 118)

  };

  const Score ThreatByRook[PIECE_TYPE_NB] = {

    S(0, 0), S(0, 25), S(40, 62), S(40, 59), S(0, 34), S(35, 48)

  };

  // ThreatByKing[on one/on many] contains bonuses for king attacks on

  // pawns or pieces which are not pawn-defended.

  const Score ThreatByKing[] = { S(3, 62), S(9, 138) };

  // Passed[mg/eg][Rank] contains midgame and endgame bonuses for passed pawns.

  // We don't use a Score because we process the two components independently.

  const Value Passed[][RANK_NB] = {

    { V(0), V(5), V( 5), V(31), V(73), V(166), V(252) },

    { V(0), V(7), V(14), V(38), V(73), V(166), V(252) }

  };

  // PassedFile[File] contains a bonus according to the file of a passed pawn

  const Score PassedFile[FILE_NB] = {

    S(  9, 10), S( 2, 10), S( 1, -8), S(-20,-12),

    S(-20,-12), S( 1, -8), S( 2, 10), S(  9, 10)

  };

  // Rank factor applied on some bonus for passed pawn on rank 4 or beyond

  const int RankFactor[RANK_NB] = {0, 0, 0, 2, 6, 11, 16};

  // KingProtector[PieceType-2] contains a bonus according to distance from king

  const Score KingProtector[] = { S(-3, -5), S(-4, -3), S(-3, 0), S(-1, 1) };

  // Assorted bonuses and penalties used by evaluation

  const Score MinorBehindPawn       = S( 16,  0);

  const Score BishopPawns           = S(  8, 12);

  const Score LongRangedBishop      = S( 22,  0);

  const Score RookOnPawn            = S(  8, 24);

  const Score TrappedRook           = S( 92,  0);

  const Score WeakQueen             = S( 50, 10);

  const Score CloseEnemies          = S(  7,  0);

  const Score PawnlessFlank         = S( 20, 80);

  const Score ThreatBySafePawn      = S(192,175);

  const Score ThreatByRank          = S( 16,  3);

  const Score Hanging               = S( 48, 27);

  const Score WeakUnopposedPawn     = S(  5, 25);

  const Score ThreatByPawnPush      = S( 38, 22);

  const Score ThreatByAttackOnQueen = S( 38, 22);

  const Score HinderPassedPawn      = S(  7,  0);

  const Score TrappedBishopA1H1     = S( 50, 50);

  #undef S

  #undef V

  // KingAttackWeights[PieceType] contains king attack weights by piece type

  const int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 78, 56, 45, 11 };

  // Penalties for enemy's safe checks

  const int QueenSafeCheck  = 780;

  const int RookSafeCheck   = 880;

  const int BishopSafeCheck = 435;

  const int KnightSafeCheck = 790;

  // Threshold for lazy and space evaluation

  const Value LazyThreshold  = Value(1500);

  const Value SpaceThreshold = Value(12222);

  // initialize() computes king and pawn attacks, and the king ring bitboard

  // for a given color. This is done at the beginning of the evaluation.

  template<Tracing T> template<Color Us>

  void Evaluation<T>::initialize() {

    const Color     Them = (Us == WHITE ? BLACK : WHITE);

    const Direction Up   = (Us == WHITE ? NORTH : SOUTH);

    const Direction Down = (Us == WHITE ? SOUTH : NORTH);

    const Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB: Rank7BB | Rank6BB);

    // Find our pawns on the first two ranks, and those which are blocked

    Bitboard b = pos.pieces(Us, PAWN) & (shift<Down>(pos.pieces()) | LowRanks);

    // Squares occupied by those pawns, by our king, or controlled by enemy pawns

    // are excluded from the mobility area.

    mobilityArea[Us] = ~(b | pos.square<KING>(Us) | pe->pawn_attacks(Them));

    // Initialise the attack bitboards with the king and pawn information

    b = attackedBy[Us][KING] = pos.attacks_from<KING>(pos.square<KING>(Us));

    attackedBy[Us][PAWN] = pe->pawn_attacks(Us);

    attackedBy2[Us]            = b & attackedBy[Us][PAWN];

    attackedBy[Us][ALL_PIECES] = b | attackedBy[Us][PAWN];

    // Init our king safety tables only if we are going to use them

    if (pos.non_pawn_material(Them) >= RookValueMg + KnightValueMg)

    {

        kingRing[Us] = b;

        if (relative_rank(Us, pos.square<KING>(Us)) == RANK_1)

            kingRing[Us] |= shift<Up>(b);

        kingAttackersCount[Them] = popcount(b & pe->pawn_attacks(Them));

        kingAdjacentZoneAttacksCount[Them] = kingAttackersWeight[Them] = 0;

    }

    else

        kingRing[Us] = kingAttackersCount[Them] = 0;

  }

  // evaluate_pieces() assigns bonuses and penalties to the pieces of a given

  // color and type.

  template<Tracing T>  template<Color Us, PieceType Pt>

  Score Evaluation<T>::evaluate_pieces() {

    const Color Them = (Us == WHITE ? BLACK : WHITE);

    const Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB

                                               : Rank5BB | Rank4BB | Rank3BB);

    const Square* pl = pos.squares<Pt>(Us);

    Bitboard b, bb;

    Square s;

    Score score = SCORE_ZERO;

    attackedBy[Us][Pt] = 0;

    if (Pt == QUEEN)

        attackedBy[Us][QUEEN_DIAGONAL] = 0;

    while ((s = *pl++) != SQ_NONE)

    {

        // Find attacked squares, including x-ray attacks for bishops and rooks

        b = Pt == BISHOP ? attacks_bb<BISHOP>(s, pos.pieces() ^ pos.pieces(QUEEN))

          : Pt ==   ROOK ? attacks_bb<  ROOK>(s, pos.pieces() ^ pos.pieces(QUEEN) ^ pos.pieces(Us, ROOK))

                         : pos.attacks_from<Pt>(s);

        if (pos.pinned_pieces(Us) & s)

            b &= LineBB[pos.square<KING>(Us)][s];

        attackedBy2[Us] |= attackedBy[Us][ALL_PIECES] & b;

        attackedBy[Us][ALL_PIECES] |= attackedBy[Us][Pt] |= b;

        if (Pt == QUEEN)

            attackedBy[Us][QUEEN_DIAGONAL] |= b & PseudoAttacks[BISHOP][s];

        if (b & kingRing[Them])

        {

            kingAttackersCount[Us]++;

            kingAttackersWeight[Us] += KingAttackWeights[Pt];

            kingAdjacentZoneAttacksCount[Us] += popcount(b & attackedBy[Them][KING]);

        }

        int mob = popcount(b & mobilityArea[Us]);

        mobility[Us] += MobilityBonus[Pt - 2][mob];

        // Bonus for this piece as a king protector

        score += KingProtector[Pt - 2] * distance(s, pos.square<KING>(Us));

        if (Pt == BISHOP || Pt == KNIGHT)

        {

            // Bonus for outpost squares

            bb = OutpostRanks & ~pe->pawn_attacks_span(Them);

            if (bb & s)

                score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & s)] * 2;

            else

            {

                bb &= b & ~pos.pieces(Us);

                if (bb)

                   score += Outpost[Pt == BISHOP][bool(attackedBy[Us][PAWN] & bb)];

            }

            // Bonus when behind a pawn

            if (    relative_rank(Us, s) < RANK_5

                && (pos.pieces(PAWN) & (s + pawn_push(Us))))

                score += MinorBehindPawn;

            if (Pt == BISHOP)

            {

                // Penalty for pawns on the same color square as the bishop

                score -= BishopPawns * pe->pawns_on_same_color_squares(Us, s);

                // Bonus for bishop on a long diagonal which can "see" both center squares

                if (more_than_one(Center & (attacks_bb<BISHOP>(s, pos.pieces(PAWN)) | s)))

                    score += LongRangedBishop;

            }

            // An important Chess960 pattern: A cornered bishop blocked by a friendly

            // pawn diagonally in front of it is a very serious problem, especially

            // when that pawn is also blocked.

            if (   Pt == BISHOP

                && pos.is_chess960()

                && (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1)))

            {

                Direction d = pawn_push(Us) + (file_of(s) == FILE_A ? EAST : WEST);

                if (pos.piece_on(s + d) == make_piece(Us, PAWN))

                    score -= !pos.empty(s + d + pawn_push(Us))                ? TrappedBishopA1H1 * 4

                            : pos.piece_on(s + d + d) == make_piece(Us, PAWN) ? TrappedBishopA1H1 * 2

                                                                              : TrappedBishopA1H1;

            }

        }

        if (Pt == ROOK)

        {

            // Bonus for aligning with enemy pawns on the same rank/file

            if (relative_rank(Us, s) >= RANK_5)

                score += RookOnPawn * popcount(pos.pieces(Them, PAWN) & PseudoAttacks[ROOK][s]);

            // Bonus when on an open or semi-open file

            if (pe->semiopen_file(Us, file_of(s)))

                score += RookOnFile[bool(pe->semiopen_file(Them, file_of(s)))];

            // Penalty when trapped by the king, even more if the king cannot castle

            else if (mob <= 3)

            {

                Square ksq = pos.square<KING>(Us);

                if (   ((file_of(ksq) < FILE_E) == (file_of(s) < file_of(ksq)))

                    && !pe->semiopen_side(Us, file_of(ksq), file_of(s) < file_of(ksq)))

                    score -= (TrappedRook - make_score(mob * 22, 0)) * (1 + !pos.can_castle(Us));

            }

        }

        if (Pt == QUEEN)

        {

            // Penalty if any relative pin or discovered attack against the queen

            Bitboard pinners;

            if (pos.slider_blockers(pos.pieces(Them, ROOK, BISHOP), s, pinners))

                score -= WeakQueen;

        }

    }

    if (T)

        Trace::add(Pt, Us, score);

    return score;

  }

  // evaluate_king() assigns bonuses and penalties to a king of a given color

  template<Tracing T>  template<Color Us>

  Score Evaluation<T>::evaluate_king() {

    const Color     Them = (Us == WHITE ? BLACK : WHITE);

    const Bitboard  Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB

                                        : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);

    const Square ksq = pos.square<KING>(Us);

    Bitboard weak, b, b1, b2, safe, unsafeChecks;

    // King shelter and enemy pawns storm

    Score score = pe->king_safety<Us>(pos, ksq);

    // Main king safety evaluation

    if (kingAttackersCount[Them] > (1 - pos.count<QUEEN>(Them)))

    {

        // Attacked squares defended at most once by our queen or king

        weak =  attackedBy[Them][ALL_PIECES]

              & ~attackedBy2[Us]

              & (attackedBy[Us][KING] | attackedBy[Us][QUEEN] | ~attackedBy[Us][ALL_PIECES]);

        unsafeChecks = 0; // Pierre-Marie Baty -- fixed variable initialization

        int kingDanger = 0;

        // Analyse the safe enemy's checks which are possible on next move

        safe  = ~pos.pieces(Them);

        safe &= ~attackedBy[Us][ALL_PIECES] | (weak & attackedBy2[Them]);

        b1 = attacks_bb<ROOK  >(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));

        b2 = attacks_bb<BISHOP>(ksq, pos.pieces() ^ pos.pieces(Us, QUEEN));

        // Enemy queen safe checks

        if ((b1 | b2) & attackedBy[Them][QUEEN] & safe & ~attackedBy[Us][QUEEN])

            kingDanger += QueenSafeCheck;

        b1 &= attackedBy[Them][ROOK];

        b2 &= attackedBy[Them][BISHOP];

        // Enemy rooks checks

        if (b1 & safe)

            kingDanger += RookSafeCheck;

        else

            unsafeChecks |= b1;

        // Enemy bishops checks

        if (b2 & safe)

            kingDanger += BishopSafeCheck;

        else

            unsafeChecks |= b2;

        // Enemy knights checks

        b = pos.attacks_from<KNIGHT>(ksq) & attackedBy[Them][KNIGHT];

        if (b & safe)

            kingDanger += KnightSafeCheck;

        else

            unsafeChecks |= b;

        // Unsafe or occupied checking squares will also be considered, as long as

        // the square is in the attacker's mobility area.

        unsafeChecks &= mobilityArea[Them];

        kingDanger +=        kingAttackersCount[Them] * kingAttackersWeight[Them]

                     + 102 * kingAdjacentZoneAttacksCount[Them]

                     + 191 * popcount(kingRing[Us] & weak)

                     + 143 * popcount(pos.pinned_pieces(Us) | unsafeChecks)

                     - 848 * !pos.count<QUEEN>(Them)

                     -   9 * mg_value(score) / 8

                     +  40;

        // Transform the kingDanger units into a Score, and subtract it from the evaluation

        if (kingDanger > 0)

        {

            int mobilityDanger = mg_value(mobility[Them] - mobility[Us]);

            kingDanger = std::max(0, kingDanger + mobilityDanger);

            score -= make_score(kingDanger * kingDanger / 4096, kingDanger / 16);

        }

    }

    // King tropism: firstly, find squares that opponent attacks in our king flank

    File kf = file_of(ksq);

    b = attackedBy[Them][ALL_PIECES] & KingFlank[kf] & Camp;

    assert(((Us == WHITE ? b << 4 : b >> 4) & b) == 0);

    assert(popcount(Us == WHITE ? b << 4 : b >> 4) == popcount(b));

    // Secondly, add the squares which are attacked twice in that flank and

    // which are not defended by our pawns.

    b =  (Us == WHITE ? b << 4 : b >> 4)

       | (b & attackedBy2[Them] & ~attackedBy[Us][PAWN]);

    score -= CloseEnemies * popcount(b);

    // Penalty when our king is on a pawnless flank

    if (!(pos.pieces(PAWN) & KingFlank[kf]))

        score -= PawnlessFlank;

    if (T)

        Trace::add(KING, Us, score);

    return score;

  }

  // evaluate_threats() assigns bonuses according to the types of the attacking

  // and the attacked pieces.

  template<Tracing T>  template<Color Us>

  Score Evaluation<T>::evaluate_threats() {

    const Color     Them     = (Us == WHITE ? BLACK      : WHITE);

    const Direction Up       = (Us == WHITE ? NORTH      : SOUTH);

    const Direction Left     = (Us == WHITE ? NORTH_WEST : SOUTH_EAST);

    const Direction Right    = (Us == WHITE ? NORTH_EAST : SOUTH_WEST);

    const Bitboard  TRank3BB = (Us == WHITE ? Rank3BB    : Rank6BB);

    Bitboard b, weak, defended, stronglyProtected, safeThreats;

    Score score = SCORE_ZERO;

    // Non-pawn enemies attacked by a pawn

    weak = (pos.pieces(Them) ^ pos.pieces(Them, PAWN)) & attackedBy[Us][PAWN];

    if (weak)

    {

        b = pos.pieces(Us, PAWN) & ( ~attackedBy[Them][ALL_PIECES]

                                    | attackedBy[Us][ALL_PIECES]);

        safeThreats = (shift<Right>(b) | shift<Left>(b)) & weak;

        score += ThreatBySafePawn * popcount(safeThreats);

    }

    // Squares strongly protected by the opponent, either because they attack the

    // square with a pawn, or because they attack the square twice and we don't.

    stronglyProtected =  attackedBy[Them][PAWN]

                       | (attackedBy2[Them] & ~attackedBy2[Us]);

    // Non-pawn enemies, strongly protected

    defended =  (pos.pieces(Them) ^ pos.pieces(Them, PAWN))

              & stronglyProtected;

    // Enemies not strongly protected and under our attack

    weak =   pos.pieces(Them)

          & ~stronglyProtected

          &  attackedBy[Us][ALL_PIECES];

    // Add a bonus according to the kind of attacking pieces

    if (defended | weak)

    {

        b = (defended | weak) & (attackedBy[Us][KNIGHT] | attackedBy[Us][BISHOP]);

        while (b)

        {

            Square s = pop_lsb(&b);

            score += ThreatByMinor[type_of(pos.piece_on(s))];

            if (type_of(pos.piece_on(s)) != PAWN)

                score += ThreatByRank * (int)relative_rank(Them, s);

        }

        b = (pos.pieces(Them, QUEEN) | weak) & attackedBy[Us][ROOK];

        while (b)

        {

            Square s = pop_lsb(&b);

            score += ThreatByRook[type_of(pos.piece_on(s))];

            if (type_of(pos.piece_on(s)) != PAWN)

                score += ThreatByRank * (int)relative_rank(Them, s);

        }

        score += Hanging * popcount(weak & ~attackedBy[Them][ALL_PIECES]);

        b = weak & attackedBy[Us][KING];

        if (b)

            score += ThreatByKing[more_than_one(b)];

    }

    // Bonus for opponent unopposed weak pawns

    if (pos.pieces(Us, ROOK, QUEEN))

        score += WeakUnopposedPawn * pe->weak_unopposed(Them);

    // Find squares where our pawns can push on the next move

    b  = shift<Up>(pos.pieces(Us, PAWN)) & ~pos.pieces();

    b |= shift<Up>(b & TRank3BB) & ~pos.pieces();

    // Keep only the squares which are not completely unsafe

    b &= ~attackedBy[Them][PAWN]

        & (attackedBy[Us][ALL_PIECES] | ~attackedBy[Them][ALL_PIECES]);

    // Add a bonus for each new pawn threats from those squares

    b =  (shift<Left>(b) | shift<Right>(b))

       &  pos.pieces(Them)

       & ~attackedBy[Us][PAWN];

    score += ThreatByPawnPush * popcount(b);

    // Add a bonus for safe slider attack threats on opponent queen

    safeThreats = ~pos.pieces(Us) & ~attackedBy2[Them] & attackedBy2[Us];

    b =  (attackedBy[Us][BISHOP] & attackedBy[Them][QUEEN_DIAGONAL])

       | (attackedBy[Us][ROOK  ] & attackedBy[Them][QUEEN] & ~attackedBy[Them][QUEEN_DIAGONAL]);

    score += ThreatByAttackOnQueen * popcount(b & safeThreats);

    if (T)

        Trace::add(THREAT, Us, score);

    return score;

  }

  // helper used by evaluate_passed_pawns to cap the distance

  template<Tracing T>

  int Evaluation<T>::king_distance(Color c, Square s) {

    return std::min(distance(pos.square<KING>(c), s), 5);

  }

  // evaluate_passed_pawns() evaluates the passed pawns and candidate passed

  // pawns of the given color.

  template<Tracing T>  template<Color Us>

  Score Evaluation<T>::evaluate_passed_pawns() {

    const Color     Them = (Us == WHITE ? BLACK : WHITE);

    const Direction Up   = (Us == WHITE ? NORTH : SOUTH);

    Bitboard b, bb, squaresToQueen, defendedSquares, unsafeSquares;

    Score score = SCORE_ZERO;

    b = pe->passed_pawns(Us);

    while (b)

    {

        Square s = pop_lsb(&b);

        assert(!(pos.pieces(Them, PAWN) & forward_file_bb(Us, s + Up)));

        bb = forward_file_bb(Us, s) & (attackedBy[Them][ALL_PIECES] | pos.pieces(Them));

        score -= HinderPassedPawn * popcount(bb);

        int r = relative_rank(Us, s);

        int rr = RankFactor[r];

        Value mbonus = Passed[MG][r], ebonus = Passed[EG][r];

        if (rr)

        {

            Square blockSq = s + Up;

            // Adjust bonus based on the king's proximity

            ebonus += (king_distance(Them, blockSq) * 5 - king_distance(Us, blockSq) * 2) * rr;